Irregular drying front

Fig. 8.11, Schematic illustration of stress formation and stress relaxation by cracking at the tip of a crack with length C. a and Oc are the externally applied stress and the stress at the crack tip respectively. Zone I is the stress relief zone, w represents the irregular drying front zone w, in zone II...

Another reason might be the more pronounced effect of the (irregular) drying front with width w in thinner specimen. If w becomes comparable with the membrane thickness, CRP and FRPl overlap and cannot be distinguished clearly. 

The heat transfer from the shelves to the sublimation front is much smaller compared with the transfer to vials with frozen liquids, as the material has an irregular form and the heat must be transferred through the already dried material (see Section 1.2.1). 

The general features of the parabolic flow law expressed by Eq. 4.36 have been widely confirmed [12]. However, the flow process itself is more complicated than that implied above. The irregular pore space of most granular materials may better be thought of as a bundle of nonuniform capillaries, all interconnected to one another. Near the advancing solvent front the liquid is pulled into the smaller pores because of the lower rc and thus r. The large pores are left dry until more liquid arrives from the rear, at which time the cavities fill one by one from smaller to larger, but by then the semidry front has moved on. Thus the level of liquid saturation of the porous bed decreases continuously as one advances toward the front. 

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